Liver and renal adipose tissues taken from male Fischer rats given Firemaster FF-1 a polybrominated biphenyl (PBB) each workday for 180 days by gavage and by diet were analysed by electron capture gas chromatography for the major component 2,4,5,2',5' hexabromobiphenyl (HXBB). For validation purposes the results of two extraction methods, viz: (a) hexane, for both liver and adipose extraction and (b) chloroform: methanol (C:M) for liver and methylene chloride (CH2Cl2) for adipose extraction were compared. As an independent monitor of these results, total tissue bromine was determined by neutron activation analysis (NAA). Extraction efficiencies were compared with each other and with the NAA values. C:M-CH2 Cl2 extractions were both reproducible and quantitative for both PBBs and tissue lipids and agreed well with NAA results. Hexane extractions gave lower lipid and HXBB values and had a high coefficient of variance (CV) indicating poorer extractability and reproducibility. No additional work done this reporting period.